The term 'egg-filled capsule' can be summarized as an ovisac, which is a six-letter word. An ovisac is a type of egg capsule that is produced by certain species of fish, amphibians, and reptiles. It is a tough, leathery structure that contains multiple eggs and provides protection for the developing embryos. The ovisac is typically attached to a substrate such as rocks or vegetation, and it can remain in place until the eggs are ready to hatch.